A Moog technician assembling a Moog Focal slip ring.

Moog Focal is currently ramping up operations and has started the hiring process to grow production capabilities, with full production expected to be reached by late 2021. The integration of aftermarket wind energy slip rings to Moog Focal’s existing solutions allows the company to provide customers with additional support across a wider range of maritime applications, including offshore wind turbines.

“A key factor in our success is our strategy of working closely with our customers, creating customized and innovative solutions that meet their specific needs,” says Shawn Taylor, General Manager of Moog Focal. “The move of this slip ring technology to Canada is a great fit for Moog and for the team in Dartmouth.”

A Moog WP7286 wind turbine slip ring like this will be produced at the Dartmouth, Canada-based Moog facility.

“We have successfully demonstrated we can compete in the global wind energy market, so it makes sense to leverage the great team and capabilities we have and apply it to the wind energy aftermarket. Not only does it deepen the technology portfolio we provide our customers, but given our heritage in providing robust solutions to the marine segment, this move also positions us to provide tremendous value to the growing offshore wind market.”

Moog Focal’s continued expansion into the renewable energy market also adds a positive impact on the Canadian economy, by promoting an increase in local job opportunities and commerce in the area.

Taylor adds, “We maintain a supply chain that is more than 90% local, providing the flexibility to adapt each solution to our customers’ specific requirements. Our supply chain has strong ties in the local area in Nova Scotia and includes key suppliers in Quebec and Ontario. Moog Focal is working with Invest in Canada (Canada’s national investment agency) to promote awareness of Moog Focal and help the company identify local government funding opportunities, support future expansion, and as a result, drive local career opportunities.”

To learn more about available career opportunities at Moog Focal, or to apply, visit https://www.careerbeacon.com/en/search/Focal-jobs

News item from Moog Focal

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In recent years wind turbines have made significant increases in size as operators and OEMs seek to optimize the costs of power generation by building fewer larger and more efficient turbines. Whilst these will produce substantially more energy than they take to manufacture, install and maintain, larger units do present significant challenges.

In mechanical terms, an increase in size means an increase in the loads generated throughout the equipment, in turn leading to more stress being imposed on virtually every component in the system, but particularly on rotating and transmission components.

Seal performance

Elastomeric rotary lip-seals of the type used to seal bearings and rotating shafts follow a long-established seal design that has changed little over the years and is now being required to achieve new levels of performance at a reduced cost. With loads on the main shaft of a large wind turbine being high enough to cause flexing and distortion of bearings, it falls to the seal to cope with any eccentricity of movement while still performing its intended duties of preventing the escape of lubricant and the ingress of contamination.

Lip-seals were also originally designed to work with oil as a lubricant, their sealing principle relying on the sealing lip running on a thin film of oil on the surface of the shaft. In modern wind turbines however, the vast majority of bearings now use high-performance greases for lubrication, bringing a whole new dynamic to the operation of the bearing seal.

With turbines now expected to achieve a working life of 20+ years and the industry driving to achieve higher load capacities, there is a demand for components to offer efficiency benefits in addition to long life.

In line with the aim of improving load factors and reducing overall generating costs, all elements of a turbine are being brought under close cost scrutiny, forcing the whole supply chain to seek ways of taking cost down while also delivering the improvements in performance demanded by increasingly harsh operating environments and the increase in turbine size.

Faced with these growing challenges, James Walker decided to take a closer look at every element of the large-diameter lip-seals required for the wind industry and see what could be done to meet current and future needs. Nothing was off-limits.

Marginal gains can provide significant benefits

As part of this investigation and in collaboration with customers in the wind industry, detailed finite element analysis (FEA) modeling and in-house dynamic testing was undertaken and led to James Walker redesigning its existing seal-lip, Walkersele. By breaking the Walkersele down into its “constituent parts” and making small but significant improvements in each of these areas, James Walker has taken an already successful and proven product and pushed it to deliver new levels of reliability and performance to meet customer demands.

Walkersele X-Gen

Identifying that a “finger” spring would provide the necessary assistance required to accommodate eccentricity/deflection and maintain a constant/linear lip-load at all points on the shaft, modeling techniques also allowed engineers to refine the spring design, optimizing it for the material and diameter of the seal.

Once the sealing element was optimized, the focus moved to the backing material and the result of a comprehensive program of experimentation and testing is a new innovative rubber/glass fiber composite material in which the glass strands are aligned circumferentially, providing enhanced dimensional stability yet retaining full flexibility that makes a large diameter seal of this construction easier to fit into its housing.

The new product, called Walkersele X-Gen, meets the challenges thrown by the increasing size of turbine designs — maintaining effective sealing against deflected shafts or housings and increased offset, plus enhanced retention of sealing forces over the full circumference of the sealing face.

Supporting operations and maintenance demands

Throughout this project James Walker has been working in partnership with a number of OEMs seeking to test factors such as seal rotation in the housing, lip load, leakage performance and life expectancy.

Walkersele X-Gen

Product development and validation testing has all been carried out in-house at the James Walker centre of excellence for elastomeric materials in the UK. Further real-life simulation testing was then carried out by OEMs using commercially produced seals on full-size housing/shaft/bearing setups.

Due to the sizes of seal required for the next generation of turbines, the joining capability of the new glass-elastomer material was also fully tested through a comprehensive regime of twist and flex motions. The conclusion drawn from these results was that the new material provides a strong homogenous bond across the area of the join, equal to or better than that observed with any alternative backing constructions.

The developed solution has demonstrated excellent capabilities in terms of maintaining shaft contact and preventing leakage or the ingress of contaminants, even when faced with eccentric running or extreme shaft deflection.

As technology progresses and demands for turbines change and increase, it is important to be able to rely on the sealing technology to reduce risk and unnecessary, unplanned maintenance. The reinvention of this particular seal aims to do that, optimizing efficiency through prolonged seal life and ultimately giving operators peace of mind.

Andras Kaldos is Product Engineering Group Manager for Key Industries at James Walker.  Andras is based at the James Walker Centre of Excellence for elastomeric materials in Cockermouth, UK, and was part of the time involved in the research, development, design and testing of Walkersele X-Gen.

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While nitrile butadiene rubber (NBR) has been a staple of wind-turbine seals for decades, advancements in polyurethane formulas, processing and seal design are quickly sidelining NBR’s place in the industry. The qualities proving most beneficial include abrasion resistance, fluid compatibility, ozone resistance, mechanical strength and the ability to maintain all these properties in low temperatures.

Polyurethane has emerged as an ideal material for seals in main/generator, pitch and yaw bearings. Nonetheless, simply swapping materials on existing designs often falls short. The seals must be engineered with polyurethane in mind.

Abrasion Resistance

One way to evaluate abrasion resistance in polyurethane is the standardized drum abrader test, such as ASTM D5963. This is often reserved for evaluating rubbers, but it is effective for polyurethanes as well, especially when comparing wear rates. Below are the abrasion-resistance-index values for various materials tested at System Seals in Cleveland. Note that while NBR and HNBR indicate ARI’s of ~1.5, polyurethane indicates an ARI of 4 to 8. This is an improvement of up to six-times.

Figure 1:  ARI of elastomers and polyurethane

Polyurethane maintains its ARI value over time and after exposure to a wide range of fluids, most notably oil-based fluids. One way to determine this is to age ASTM D5963 abrasion samples in fluids for 90 days at 100°C (80°C for water-based fluids) and repeat the test every 30 days. Below are typical results, but confirmation for each fluid is recommended.

Figure 2: ARI retention of NBR and hydrolysis-resistant PU after ageing in distilled water at 80°C

Figure 3: ARI retention of NBR and hydrolysis-resistant PU after ageing in distilled mineral oil at 100°C

Fluid Compatibility

While spec sheets indicate out-of-the-box fluid compatibility, accelerated ageing tests – or years of application run time – should determine long-term performance and stability of a material exposed to a particular fluid. System Seals performs 90-day fluid compatibility tests, versus the industry-standard 168-hour tests, as System Seals has consistently found significant changes in critical material properties well after 168-hours of fluid contact.

Compared to NBR, custom-formulated polyurethanes demonstrate improved fluid resistance with the most common greases in the wind industry. Below is a compatibility chart for these popular greases.

Figure 4: Ageing scores in grease; lower is better

Ozone Resistance

NBR is notoriously susceptible to ozonolysis – when ozone molecules separate the chemical bonds in unsaturated NBR. Ozone cracking is common when NBR experiences even minimal strains. One solution is to infuse NBR with waxes, which create an anti-ozone barrier that protects the NBR. Unfortunately, waxes do not change the chemical bonding of NBR. If NBR is exposed to environmental conditions that remove the wax, it again becomes susceptible to degradation. Some specialty polyurethanes used in wind energy seals are naturally ozone resistant.

Mechanical Properties

Polyurethane has tensile modulus, strength and elongation two- to three-times higher than most NBRs. Because of this, polyurethane seals are capable of resisting greater mechanical deformation and sustaining higher mechanical loads.

A typical NBR has a tensile modulus of 10-15 MPa and a tensile strength of 20 MPa. Most polyurethanes have a modulus of 45-60 MPa and tensile strength of 50-60 MPa. This translates to a stiffer material that is less compliant than NBR, meaning greater shape retention under pressure and higher stress-load capability.

Thermal Properties

High temperatures are typically not a concern in wind applications. However, depending on location and elevation, -40°C minimum temperature is not uncommon. A minimum service temperature for standard NBR could be -20° C, while many wind-power polyurethanes are unaffected down to -40°C, as determined by dynamical mechanical analysis.

Figure 5: Comparison of glass transition temperature (Tg) to determine minimum service temperature

Figure 6: Radar plot of normalized property scores, higher is desirable

Current Applications

Polyurethane is a natural choice for wind-energy seals because it has greater mechanical properties, better ozone resistance, reduced wear rates and lower service temperatures. Below are two application families for which polyurethane is well suited. The left image shows simulated deformation and contact features of a polyurethane pitch bearing seal. The right image features System Seals’ Vortex seal, a main bearing seal that continuously pumps grease back into the reservoir at the bearing spins.

Figure 7: pitch seal FEA (left) and Vortex main bearing sea (right)

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